I don't mind seeing the edit notice if they do. And if the are editing, I'll assume it's not because it's a mistake in id ing a mineral. I would think it's because of uncalled for content, and therefore the member should be suspended.
The coherence of replies to threads can look a little strange if original posts are changed. Knowing some post has been edited can provide a reason for some of this. Personally I would be more inclined to totally remove the option for a person to edit their messages.